This invention relates broadly to ergometers of the bicycle type for subjecting a patient being examined to physical stress.
More particularly, this invention relates to an erogmeter which includes a direct current generator which is operated by the patient being tested. Permanent magnets are provided to produce an exciter field. A loading device which is connected to the outlet of the generator includes an electronic load adjusting device for keeping the electrical load of the generator at the pre-set value. An electronic control is fed by the generator which determines the nominal value to be set in the loading device by taking into consideration the additional load caused by mechanical losses of the machine.
In the case of a known ergometer of this kind (German Pat. No. DT-OS 1,616,895), the nominal value is composed of a constant voltage produced with the help of a circuit connected to the generator and a voltage proportional to the speed of the generator which is produced by means of a tacho-machine. However, such a device is relatively expensive and suffers from the additional disadvantage that the output produced by the patient is not independent of the speed where the ergometer is provided with a fan for cooling the generator, the mechanical losses are related to the speed, i.e., a quadratic dependence. If no fan is provided, the generator must be of considerably larger design which contributes to the cost of the apparatus.
In view of the foregoing, it is apparent that there still exists a need for an ergometer which is not subject to the aforementioned disadvantages. It is therefore a primary object of this invention to provide an ergometer which is of relatively low cost and which can be operated in a manner so that the output is kept independent of the speed for all selected output values.